Information transfer using discrete-frequency signals and instantaneous frequency measurement

ABSTRACT

A method of receiving information is provided. The method, performed at a system for information transfer, includes receiving a first signal pulse and determining a first frequency band associated with the first signal pulse. The method includes, in accordance with a determination that the first frequency band is a respective frequency band in a first set of frequency bands, determining, from a predefined set of symbols associated with the first set of frequency bands, a first symbol associated with the first frequency band and represented by the first signal pulse. The first set of frequency bands includes a second frequency band that is a nearest frequency band in the first set of frequency bands to the first frequency band. The first frequency band has a first center frequency; the second frequency band has a second center frequency; and a difference between the first center frequency and the second center frequency exceeds a frequency difference threshold.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/126,361, filed Sep. 10, 2018, entitled “Information Transfer UsingDiscrete-Frequency Signals and Instantaneous Frequency Measurement,”which claims priority to U.S. Provisional Application Ser. No.62/557,418, filed Sep. 12, 2017, entitled “Information Transfer UsingDiscrete-Frequency Continuous Waves and Instantaneous FrequencyMeasurement,” both of which are incorporated by reference herein intheir entireties.

TECHNICAL FIELD

This relates generally to information transfer through modulation ofelectronic signals, including but not limited to discrete-frequencysignals and instantaneous frequency measurement of signals.

BACKGROUND

The transfer of information between devices is widely achieved throughthe modulation and transmission of electronic signals, for example by atransmitter, and the receipt and demodulation of the transmittedelectronic signals, for example, by a receiver. Conventional techniquesfor modulation of electronic signals are cumbersome, inefficient, andlimited. In some cases, conventional modulation methods are constrainedby limited signal-to-noise ratios of transmitted signals, often due tolimits on transmission power levels due to transmitter design or toregulatory limits. In some cases, conventional modulation methodsrequire wide hands of frequency spectrum, which are limited and can bedifficult to obtain. In some cases, because receivers have limitedability to accurately determine the frequency of a received signal,wider frequency bands are used for each unit of information, whichreduces the information transmission rate obtainable per unit of aparticular band of frequency spectrum.

SUMMARY

Accordingly, there is a need for methods of information transfer, andsystems and devices for carrying out such methods, that better utilizeavailable frequency spectrum, improve receiver accuracy, and achievehigher rates of information transmission per unit of available frequencyspectrum.

The above deficiencies and other problems associated with conventionalinformation transfer approaches are reduced or eliminated by thedisclosed methods, devices, and systems. In accordance with someembodiments, a method of receiving information includes receiving afirst signal pulse and determining a first frequency band associatedwith the first signal pulse. The method includes, in accordance with adetermination that the first frequency band is a respective frequencyband in a first predefined set of frequency bands, determining, from apredefined set of symbols, a first symbol associated with the firstfrequency band and represented by the first signal pulse, and providingthe first symbol. In some embodiments, each frequency band in the firstpredefined set of frequency bands is associated with a distinctrespective symbol in the predefined set of symbols. In some embodiments,frequency bands in the first predefined set of frequency bands, inaggregate, are not contiguous.

In some embodiments, the method further includes, after at least apredefined amount of time since receiving the first signal pulse,receiving a second signal pulse and determining a second frequency bandassociated with the second signal pulse. In some embodiments, the methodfurther includes, in accordance with a determination that the secondfrequency band is a respective frequency band in the first predefinedset of frequency bands, determining, from the predefined set of symbols,a second symbol associated with the second frequency band andrepresented by the second signal pulse and providing the second symbol.

In some embodiments, the first predefined set of frequency bands areassociated with the predefined set of symbols using a lookup table. Insome embodiments, determining the first symbol associated with the firstfrequency band includes selecting the respective symbol associated withthe first frequency band in the lookup table.

In some embodiments, a duration of the first signal pulse is less than apredetermined duration.

In some embodiments, a length of the first signal pulse is less than onefull wavelength. In some embodiments, determining the first frequencyband associated with the first signal pulse includes determining a phaseof the first signal pulse at a respective time, determining a firstfrequency of the first signal pulse based on the determined phase of thefirst signal pulse at the respective time and on a rate of change withrespect to time of the first signal pulse at the respective time, anddetermining that the first frequency of the first signal pulse is in thefirst frequency band.

In some embodiments, the predefined set of symbols includes two or moresymbols associated with the first frequency band, each symbol of the twoor more symbols associated with a respective pulse duration. In someembodiments, the method further includes determining a first pulseduration of the first signal pulse. In some embodiments, determining thefirst symbol includes selecting the first symbol from the two or moresymbols associated with the first frequency band based on the firstpulse duration.

In some embodiments, the first signal pulse is received at a pluralityof input channels of a receiver, each input channel associated with arespective frequency band in the first predefined set of frequencybands. In some embodiments, determining the first frequency bandassociated with the first signal pulse includes measuring channel powerof each respective input channel, and identifying a respective inputchannel having a highest measured channel power.

In some embodiments, determining the first frequency band associatedwith the first signal pulse includes receiving the first signal pulse ata first frequency detection stage and determining, using the firstfrequency detection stage, a first frequency range that includes thefirst frequency of the first signal pulse. In some embodiments, themethod further includes, after determining the first frequency range,receiving the first signal pulse at a second frequency detection stageand determining, within the first frequency range, using the secondfrequency detection stage, a second frequency range that includes thefirst frequency of the first signal pulse. In some embodiments, thesecond frequency range is smaller than the first frequency range and thefirst frequency band corresponds to the second frequency range.

In some embodiments, the method further includes, before receiving thefirst signal pulse, obtaining a third signal pulse, determining a thirdfrequency of the third signal pulse, and comparing the third frequencyto a predefined calibration frequency to determine a difference betweenthe third frequency and the predefined calibration frequency. In someembodiments, determining the first frequency band of the first signalpulse includes determining an initial frequency of the first signalpulse, determining an adjusted frequency of the first signal pulse basedon applying the determined difference to the initial frequency, anddetermining the first frequency band based on the adjusted frequency.

In some embodiments, the first predefined set of frequency bandsincludes a first respective frequency band and a second respectivefrequency band that is a nearest frequency band in the first predefinedset of frequency bands to the first respective frequency band. In someembodiments, the first respective frequency band has a first centerfrequency and the second respective frequency band has a second centerfrequency. In some embodiments, a difference between the first centerfrequency and the second center frequency exceeds a predefined frequencydifference threshold.

In some embodiments, the method further includes, after receiving thefirst signal pulse, receiving a control signal associating a secondpredefined set of frequency bands with the predefined set of symbols. Insome embodiments, the second predefined set of frequency bands isdistinct from the first predefined set of frequency bands. In someembodiments, each frequency band in the second predefined set offrequency bands is associated with a distinct respective symbol in thepredefined set of symbols. In some embodiments, frequency bands in thesecond predefined set of frequency bands, in aggregate, are notcontiguous. In some embodiments, the method further includes, afterreceiving the control signal, receiving a fourth signal pulse, anddetermining a third frequency band associated with the fourth signalpulse. In some embodiments, the method includes, in accordance with adetermination that the third frequency band is a respective frequencyband in the second predefined set of frequency bands, determining, fromthe predefined set of symbols, a third symbol associated with the thirdfrequency band and represented by the fourth signal pulse, and providingthe third symbol.

In accordance with some embodiments, a method of receiving informationincludes receiving a first signal pulse, determining a first frequencyband associated with the first signal pulse, and determining a firstpulse duration of the first signal pulse. The method includes, inaccordance with a determination that the first frequency band is arespective frequency band in a first predefined set of frequency bands,and in accordance with a determination that the first pulse duration isa respective pulse duration in a first predefined set of pulsedurations, determining, from a predefined set of symbols, a first symbolassociated with the first frequency band and with the first pulseduration, and represented by the first signal pulse. The method alsoincludes providing the first symbol. In some embodiments, each frequencyband in the first predefined set of frequency bands is associated withtwo or more distinct symbols in the predefined set of symbols. In someembodiments, each of the two or more distinct symbols associated with arespective frequency band is associated with a distinct respective pulseduration in the first predefined set of pulse durations.

In accordance with some embodiments, a system for information transferincludes a receiver configured to receive a first signal pulse. Thesystem further includes processing circuitry configured to receive afirst signal pulse and determine a first frequency band associated withthe first signal pulse. In accordance with a determination that thefirst frequency band is a respective frequency band in a firstpredefined set of frequency bands, the processing circuitry isconfigured to determine, from a predefined set of symbols, a firstsymbol associated with the first frequency band and represented by thefirst signal pulse, and to provide the first symbol. In someembodiments, each frequency band in the first predefined set offrequency bands is associated with a distinct respective symbol in thepredefined set of symbols. In some embodiments, frequency bands in thefirst predefined set of frequency bands, in aggregate, are notcontiguous. In some embodiments, the system for information transfer isconfigured to perform any of the methods for receiving information, asdescribed herein.

In accordance with some embodiments, a method of transmittinginformation includes obtaining a first symbol, in a predefined set ofsymbols, for transmission. The method further includes determining afirst frequency band, in a first predefined set of frequency bands,associated with the first symbol, and transmitting a first signal pulsehaving a first frequency in the first frequency band. In someembodiments, each frequency band in the first predefined set offrequency bands is associated with a distinct respective symbol in thepredefined set of symbols. In some embodiments, frequency bands in thefirst predefined set of frequency bands, in aggregate, are notcontiguous.

In some embodiments, the method further includes obtaining a secondsymbol, in the predefined set of symbols, for transmission, anddetermining a second frequency band, in the first predefined set offrequency bands, associated with the second symbol. In some embodiments,the method further includes, after at least a predefined amount of timesince transmitting the first signal pulse, transmitting a second signalpulse having a second frequency in the second frequency band.

In some embodiments, the method includes, after transmitting the firstsignal pulse, transmitting a control signal associating a secondpredefined set of frequency bands with the predefined set of symbols. Insome embodiments, the second predefined set of frequency bands isdistinct from the first predefined set of frequency bands and eachfrequency band in the second predefined set of frequency bands isassociated with a distinct respective symbol in the predefined set ofsymbols. In some embodiments, frequency bands in the second predefinedset of frequency bands, in aggregate, are not contiguous. In someembodiments, the method further includes, after transmitting the controlsignal, obtaining a third symbol, in the predefined set of symbols, fortransmission and determining a third frequency band, in the secondpredefined set of frequency bands, associated with the third symbol. Insome embodiments, the method further includes transmitting a thirdsignal pulse having a third frequency in the third frequency band.

In some embodiments, the method further includes, prior to transmittingthe control signal associating the second predefined set of frequencybands with the predefined set of symbols, determining that a spectraldensity of a respective frequency band in the first predefined set offrequency bands satisfies a predefined threshold value, and identifying,from the predefined set of symbols, a respective symbol that isassociated with the respective frequency band in the first predefinedset of frequency bands. In some embodiments, the method includesdetermining that a spectral density of a fourth frequency band, outsideof the first predefined set of frequency bands, is below the predefinedthreshold value. In some embodiments, the second predefined set offrequency bands includes the fourth frequency band, and the respectivesymbol in the predefined set of symbols is associated with the fourthfrequency bond in the second predefined set of frequency bands.

In some embodiments, the first predefined set of frequency bands areassociated with the predefined set of symbols using a lookup table. Insome embodiments, determining the first frequency band associated withthe first symbol includes selecting the respective frequency bandassociated with the first symbol in the lookup table.

In some embodiments, the predefined set of symbols includes two or moresymbols associated with the first frequency band, each symbol of the twoor more symbols associated with a respective pulse duration. In someembodiments, the method includes determining a first pulse durationbased on the first symbol of the two or more symbols. In someembodiments, a pulse duration of the first signal pulse corresponds tothe first pulse duration.

In some embodiments, the method further includes, before transmittingthe first signal pulse, transmitting a plurality of successive pulseshaving one or more calibration frequencies.

In accordance with some embodiments, a method of transmittinginformation includes obtaining a first symbol, in a predefined set ofsymbols, for transmission. The method includes determining a firstfrequency band, in a first predefined set of frequency bands, associatedwith the first symbol. The method also includes determining a firstpulse duration, in a first predefined set of pulse durations, associatedwith the first symbol. The method includes transmitting a first signalpulse having the first pulse duration and having a first frequency inthe first frequency band. In some embodiments, each frequency band inthe first predefined set of frequency bands is associated with two ormore distinct symbols in the predefined set of symbols. In someembodiments, each of the two or more distinct symbols associated with arespective frequency band is associated with a distinct respective pulseduration in the first predefined set of pulse durations.

In accordance with some embodiments, a system for information transferincludes processing circuitry configured to obtain a first symbol, in apredefined set of symbols, for transmission, and determine a firstfrequency band, in a first predefined set of frequency bands, associatedwith the first symbol. The system further includes a transmitter,configured to transmit a first signal pulse having a first frequency inthe first frequency band. In some embodiments, each frequency band inthe first predefined set of frequency bands is associated with adistinct respective symbol in the predefined set of symbols. In someembodiments, frequency bands in the first predefined set of frequencybands, in aggregate, are not contiguous. In some embodiments, the systemfor information transfer is configured to perform any of the methods fortransmitting information, as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various described embodiments,reference should be made to the Detailed Description below, inconjunction with the following drawings.

FIG. 1 is a block diagram illustrating an example implementation of acommunications system, in accordance with some embodiments.

FIG. 2A is a block diagram illustrating an example implementation of atransmitting system, in accordance with some embodiments.

FIG. 2B is a block diagrams illustrating an example implementation of areceiving system, in accordance with some embodiments.

FIGS. 3A-3B are block diagrams illustrating example lookup tablesassigning frequencies to symbols and symbol data, in accordance withsome embodiments.

FIG. 3C is a conceptual diagram showing example allocations of afrequency spectrum, in accordance with some embodiments.

FIG. 3D illustrates an example sequence of discrete-frequency signals,is accordance with some embodiments.

FIG. 3E illustrates example variations in signal duration forrepresenting multiple symbols using a given frequency.

FIG. 4 is a block diagram illustrating an example implementation offrequency detection circuitry, in accordance with some embodiments.

FIGS. 5A-5C are flow diagrams illustrating an example method ofreceiving information, in accordance with some embodiments.

FIGS. 6A-6B are flow diagrams illustrating an example method oftransmitting information, in accordance with some embodiments.

In accordance with common practice, the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may not depict all the elements of agiven system, method or device, or may depict relevant features orportions of an element without depicting the full extent of the element.Finally, like reference numerals refer to corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. In the following detaileddescription, numerous specific details are set forth to provide athorough understanding of the various described embodiments. However, itwill be apparent to one of ordinary skill in the art that the variousdescribed embodiments may be practiced without these specific details.In other instances, well-known methods, procedures, components,circuits, and networks have not been described in detail so as not tounnecessarily obscure aspects of the embodiments.

It will also be understood that, although the terms “first,” “second,”etc. may be used herein to describe various element, these elementshould not be limited by these terms. These terms are only used todistinguish one element from another. For example, a first signal couldbe termed a second signal, and, similarly, a second signal could betermed a first signal, without changing the meaning of the description,so long as all occurrences of the “first signal” are renamedconsistently and all occurrences of the “second signal” are renamedconsistently. The first signal and the second signal are both signals,but they are not the same signal, unless the context clearly indicatesotherwise.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the claims. Asused in the description of the embodiments and the appended claims, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willalso be understood that the term “and/or” as used herein refers to andencompasses any and all possible combinations of one or more of theassociated listed items. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

As used herein, the phrase “at least one of A, B and C” is to beconstrued to require one or more of the listed items, and this phrasereads on a single instance of A alone, a single instance of B alone, ora single instance of C alone, while also encompassing combinations ofthe listed items such as “one or more of A and one or more of B withoutany of C,” and the like.

As used herein, the term “if” may be construed to mean “when” or “upon”or “in response to determining” or “in accordance with a determination”or “in response to detecting” that a stated condition precedent is true,depending on the context. Similarly, the phrase “if it is determined[that a stated condition precedent is true]” or “if [a stated conditionprecedent is true]” or “when [a stated condition precedent is true]” maybe construed to mean “upon determining” or “in response to determining”or “in accordance with a determination” or “upon detecting” or “inresponse to detecting” that the stated condition precedent is true,depending on the context.

FIG. 1 is a block diagram illustrating an example implementation ofcommunications system 100, in accordance with some embodiments. In someembodiments, communications system 100 is used to perform any of themethods described herein. While some example features are illustrated,various other features have not been illustrated for the sake of brevityand so as not to obscure pertinent aspects of the example embodimentsdisclosed herein. To that end, as a non-limiting example, communicationssystem 100 includes a transmitting system 120 (sometimes called atransmitting device), which is used to transmit data (e.g., to areceiving system), and a receiving system 140 (sometimes called areceiving device), which is used to receive data (e.g., transmitted by atransmitting system).

In some embodiments, transmitting system 120 includes processingcircuitry 102. In some embodiments, processing circuitry 102 isimplemented using one or more processors (or processor cores) (e.g.,CPUs, microprocessors, microcontrollers, digital signal processors(DSPs), or the like) configured to execute instructions in one or moreprograms (e.g., stored in processing circuitry 102, such as in one ormore memory components of processing circuitry 102, or stored in memoryseparate from and communicatively coupled with processing circuitry 102)for performing operations described herein. In some embodiments,processing circuitry 102 is implemented using hardware circuitry such asone or more field-programmable gate arrays (FPGAs) orapplication-specific integrated circuits (ASICs) configured to performoperations described herein.

In some embodiments, transmitting system 120 includes lookup table 104.In some embodiments, lookup table 104 stores information associatingsymbols (which represent units of data) with frequencies representingthe symbols, and, in some embodiments, associating units of data withthe symbols representing the data (e.g., as described in further detailherein with reference to FIGS. 3A-3B). In some embodiments, processingcircuitry 102 is communicatively coupled with lookup table 104. In someembodiments, lookup table is stored in a storage medium, such asnon-volatile memory (e.g., solid-state memory, flash memory, that can bepart of or separate from processing circuitry 102) or volatile memory(e.g., a cache of processing circuitry 102) in transmitting system 120.In some embodiments, processing circuitry 102 identifies data fortransmission, and, using information from lookup table 104, identifiesfrom the data one or more units of data for transmission (e.g., one ormore groups of bits of data) corresponding to one or more predefinedsymbols. In some embodiments, processing circuit 102 uses informationobtained from lookup table 104 to determine respective frequencies atwhich to transmit respective signals representing the one or moresymbols, each representing a unit of the data for transmission.

In some embodiments, transmitting system 120 includes frequencygeneration circuitry 106. In some embodiments, frequency generationcircuitry 106 is used to generate respective signals at respectivefrequencies determined by processing circuitry 102, to represent one ormore symbols representing data. To that end, in some embodiments,frequency generation circuitry 106 includes variable-frequencyoscillator (VFO) 108, upconverter 110, and/or amplifier 112. In someembodiments, VFO 108 is used to generate signals (e.g., continuous wavesignals or pulses) at respective frequencies. In some embodiments, VFO108 generates sinusoidal signals. In some embodiments, VFO 108 generatessquare waves. In some embodiments, VFO 108 generates signals that havefrequencies corresponding to the frequencies in lookup table 104 and arerepresentative of symbols. In some embodiments, the signals generated byVFO 108 are optionally converted to higher frequencies for transmissionusing upconverter 110 (e.g., in situations where higher-frequency signaltransmission is preferred over lower-frequency signal transmission). Insome embodiments, amplifier 112 receives signals from frequencygeneration circuitry 106, optionally via upconverter 110, and amplifiesthe signals (e.g., the signal amplitude) prior to transmission.

In some embodiments, transmitting system 120 includes transmitter 114.In some embodiments, transmitter 114 is used to transmit signals thathave been produced by frequency generation circuitry 106 (optionally inconjunction with upconverter 110 and/or amplifier 112) in accordancewith respective frequencies determined by processing circuitry 102, andoptionally amplified using amplifier 112. In some embodiments,transmitter 114 is, or includes, an antenna.

In some embodiments, one or more signals transmitted by transmittingsystem 120 (e.g., by transmitter 114), are received at receiving system140. More specifically, in some embodiments, the one or more signals arereceived at receiver 118 of receiving system 140. In some embodiments,receiver 118 is, or includes, an antenna. In some embodiments, receiver118 is communicatively coupled with frequency determination circuitry116. In some embodiments, frequency determination circuitry 116determines respective frequencies of one or more signals received byreceiver 118 (e.g., from transmitting system 120).

In some embodiments, frequency determination circuitry 120 includesamplifier 132, downconverter 130, frequency detector 128, and/or errorcorrection circuitry 126. In some embodiments, signals received) byreceiver 118 are amplified by amplifier 132 prior to determining thefrequencies of the received signals. In some embodiments, such as thosein which a transmitting system uses an upconverter, correspondingdownconverter 130 is used to convert received signals to signals thathave lower frequencies, which in turn are used for detection anddecoding. In some embodiments, frequency detector 128 receives signalsfrom receiver 118 (optionally via downconverter 130 and/or amplifier132) and determines the frequencies of the received signals.

In some embodiments, error correction circuitry 126 receives detectedfrequencies from frequency detector 128 and determines a correctionfactor (e.g., an offset) corresponding to the determined frequencies. Insome embodiments, error correction circuitry 126 is used to calibrate orrecalibrate frequency detector 128. In some such embodiments, errorcorrection circuitry 126 compares a detected frequency received fromfrequency detector 128 to a known, expected frequency, to determine acorrection factor for the determined frequency. In some embodiments,error correction circuitry 126 is used to correct a detected frequencyby applying a previously-determined correction factor to a detectedfrequency received from frequency detector 128.

In some embodiments, frequency determination circuitry 120 (e.g.,frequency detector 128, optionally in conjunction with error correctioncircuitry 126) output frequencies that have been determined for receivedsignals to processing circuitry 122 of receiving system 140. In someembodiments, processing circuitry 122 is implemented using one or moreprocessors configured to execute instructions in one or more programs,or using hardware circuitry, as described above with reference toprocessing circuitry 102 of transmitting system 120.

In some embodiments, receiving system 140 includes lookup table 124. Insome embodiments, lookup table 124 stores information associatingsymbols (which represent units of data) with frequencies representingthe symbols, and, in some embodiments, associating units of data withthe symbols representing the data (e.g., similar to lookup table 104 oftransmitting system 120, and as described in further detail herein withreference to FIGS. 3A-3B. In some embodiments, processing circuitry 122is communicatively coupled with lookup table 124. In some embodiments,lookup table is stored in a storage medium, such as non-volatile memory(e.g., solid-state memory, flash memory, that can be part of or separatefrom processing circuitry 122) or volatile memory (e.g., a cache ofprocessing circuitry 122) in receiving system 140. In some embodiments,processing circuitry 122 uses information from lookup table 124 todetermine respective symbols associated with respective frequenciesreceived from frequency determination circuitry 120 (e.g., respectivefrequencies of signals received at receiver 118). In some embodiments,processing circuitry 122 uses information from lookup table 124 toidentify one or more units of received data represented by thedetermined symbols. In some embodiments, processing circuitry 122processes the one or more units of received data. In some embodiments,processing circuitry 122 aggregates (e.g., concatenates) multiple unitof received data and processes the aggregated data.

FIG. 2A is a block diagram illustrating an example implementation of atransmitting system 200, in accordance with some embodiments. In someembodiments, transmitting system 200 is used in communication system100, FIG. 1 (e.g., in place of transmitting system 120) for transmittingsignals representing data (e.g., information for transmission).

In some embodiments, transmitting system 200 includes one or moreprocessing units 202 (e.g., sometimes called processors or CPUs, andimplemented using processors or processing cores, as described above)for executing modules, programs and/or instructions stored in memory 206for performing operations described herein; memory 206; and one or morecommunication busts 208 for interconnecting these components.Communication buses 208 optionally include circuitry (sometimes called achipset) that interconnects and controls communications between systemcomponents. In some embodiments, transmitting system 200 includestransmitter 114 and frequency generation circuitry 106 (e.g., asdescribed herein with reference to FIG. 1).

In some embodiments, memory 206 includes high-speed random accessmemory, such as DRAM, SRAM, DDR RAM or other random access solid statememory devices, and may include non-volatile memory, such as one or moremagnetic disk storage devices, optical disk storage devices, flashmemory devices, or other non-volatile solid state storage devices.Memory 206 optionally includes one or more storage devices remotelylocated from processors 202. In some embodiments, memory 206, or thenon-volatile memory device(s) within memory 206, includes anon-transitory computer readable storage medium. In some embodiments,memory 206, or the computer readable storage medium of memory 206,stores the following programs, modules, and data structures, or a subsetor superset thereof:

-   -   lookup table 104, used for storing associations of units of data        to symbols and frequencies (e.g., as described herein with        reference to FIG. 1);    -   data processing module 212, used for identifying units of data        from aggregated data, identifying symbols associated with the        identified units of data, and identifying frequencies        representing the identified symbols and identified units of        data;    -   frequency generation control module 214, used for controlling        generation of signals at identified frequencies (e.g.,        identified by data processing module 212) using frequency        generation circuitry 106, optionally including:        -   training module 216, used for controlling generation of one            or more calibration signals (sometimes called a “training            sequence”) for transmission to a receiving system and used            to correct for or mitigate transmission errors between            transmitting system 200 and the receiving system; and    -   frequency assignment module 218, used for identifying        frequencies and/or frequency bands that are available for        transmission; and assigning units of data and symbols to a set        of frequency bands (or to respective frequencies within the set        of frequency bands), and, in some embodiments, reassigning units        of data and symbols to different sets of frequency bands (or        frequencies), and for updating lookup table 104 accordingly.

Each of the above identified elements may be stored in one or more ofthe previously mentioned memory devices that together form memory 206,and corresponds to one or more sets of instructions for performing afunction described above. The above identified modules or programs(i.e., sets of instructions) need not be implemented as separatesoftware programs, procedures; or modules, and thus various subsets ofthese modules may be combined or otherwise rearranged in variousembodiments. In some embodiments, memory 206 may store a subset of themodules and data structures identified above. In some embodiments,memory 206 may store additional modules and data structures notdescribed above. In some embodiments, the programs, modules, and datastructures stored in memory 206, or the computer readable storage mediumof memory 206, provide instructions for implementing respectiveoperations in the methods described below with reference to FIGS. 5A-5Cand 6A-6B.

Although FIG. 2A shows transmitting system 200, FIG. 2A is intended moreas a functional description of the various features that may be presentin a transmitting system than as a structural schematic of theembodiments described herein. In practice, and as recognized by those ofordinary skill in the art, items shown separately could be combined andsome items could be separated. Further, in some embodiments, one or moremodules of transmitting system 200 are implemented in transmittingsystem 120 (e.g., in processing circuitry 102) of FIG. 1.

FIG. 2B is a block diagram illustrating an example implementation of areceiving system 220, in accordance with some embodiments. In someembodiments, receiving system 220 is used in communication system 100,FIG. 1 (e.g., in place of receiving system 140) for receiving signalsrepresenting data (e.g., transmitted information).

In some embodiments, receiving system 220 includes one or moreprocessing units 222 (e.g., sometimes called processors or CPUs, andimplemented using processors or processing cores, as described above)for executing modules, programs and/or instructions stored in memory 226for performing operations described herein; memory 226; and one or morecommunication buses 228 for interconnecting these components.Communication buses 228 optionally include circuitry (sometimes called achipset) that interconnects and controls communications between systemcomponents. In some embodiments, receiving system 220 includes receiver118 and frequency determination circuitry 120 (e.g., as described hereinwith reference to FIG. 1).

In some embodiments, memory 226 includes high-speed random accessmemory, such as DRAM, SRAM, DDR RAM or other random access solid statememory devices, and may include non-volatile memory, such as one or moremagnetic disk storage devices, optical disk storage devices, flashmemory devices, or other non-volatile solid state storage devices.Memory 226 optionally includes one or more storage devices remotelylocated from processors 222. In some embodiments, memory 226, or thenon-volatile memory device(s) within memory 226, includes anon-transitory computer readable storage medium. In some embodiments,memory 226, or the computer readable storage medium of memory 226,stores the following programs, modules, and data structures, or a subsetor superset thereof:

lookup table 124, used for storing associations of units of data tosymbols and frequencies (e.g., as described herein with reference toFIG. 1);

data processing module 232, used for identifying symbols represented bydetected frequencies, identifying units of data represented by theidentified symbols, and aggregating the units of data for processing;

-   -   frequency detection control module 234, used for controlling        frequency determination circuitry 120 to detect frequencies of        received signals (e.g., from receiver 118), optionally        including:        -   calibration module 236, used for controlling, generating,            and processing signals used for internal calibration of            frequency determination circuitry 120 (e.g., used local            calibration of receiving system 220); and        -   training module 238, used for processing one or more            calibration signals (sometimes called a “training sequence”)            received from a transmitting system and used to correct for            or mitigate transmission errors between the transmitting            system and receiving system 220.    -   frequency assignment module 240, used for updating lookup table        124 with updated assignments of units of data and symbols to a        different set of frequency bands (or to respective frequencies        within the set of frequency bands) received from a transmitting        system.

Each of the above identified elements may be stored in one or more ofthe previously mentioned memory devices that together form memory 226,and corresponds to one or more sets of instructions for performing afunction described above. The above identified modules or programs(i.e., sets of instructions) need not be implemented as separatesoftware programs, procedures, or modules, and thus various subsets ofthese modules may be combined or otherwise rearranged in variousembodiments. In some embodiments, memory 226 may store a subset of themodules and data structures identified above. In some embodiments,memory 226 may store additional modules and data structures notdescribed above. In some embodiments, the programs, modules, and datastructures stored in memory 225, or the computer readable storage mediumof memory 226, provide instructions for implementing respectiveoperations in the methods described below with reference to FIGS. 5A-5Cand 6A-6B.

Although FIG. 2B shows receiving system 220, FIG. 2B is intended more asa functional description of the various features that may be present ina receiving system than as a structural schematic of the embodimentsdescribed herein. In practice, and as recognized by those of ordinaryskill in the art, items shown separately could be combined and someitems could be separated. Further, in some embodiments, one or moremodules of receiving system 220 are implemented in receiving system 140(e.g., in processing circuitry 122) of FIG. 1.

FIGS. 3A-3B are block diagrams illustrating example lookup tablesassigning frequencies to symbols and symbol data, in accordance withsome embodiments. In particular, FIG. 3A illustrates example lookuptable 104 for use in a transmitting system (e.g., transmitting system120, FIG. 1, or transmitting system 200, FIG. 2A). Lookup table 104assigns symbol data (e.g., each representing four bits of information,such as the data values 0000, 0001, 0010, etc.) to each of N symbols(e.g., symbols 0 through N−1). Each symbol is associated with arespective frequency. As shown in FIG. 3A, each symbol is associatedwith a nominal center frequency in a frequency band that is 62.5 kHzwide. It is noted that the frequency band for symbol 2 and the frequencyband for symbol 3 are not contiguous. That is, the nominal centerfrequency of the frequency band immediately adjacent to and above thefrequency band for symbol 2 is 10.419 kHz, but this frequency is notassigned to any of the N symbols. Accordingly, the assigned frequencybands, in aggregate, are not contiguous. In some embodiments, lookuptable 104 is used by a transmitting system to identify, from data fortransmission, units of data corresponding to symbols (e.g., the four-bitdata values 0000, 0001, etc.) and, in turn, frequencies representing thesymbols.

Analogously, FIG. 3B illustrates example lookup table 124 for use in areceiving system (e.g., receiving system 140, FIG. 1, or receivingsystem 220, FIG. 2B). Lookup table 124 assigns respective frequencies toeach of the N symbols (e.g., symbols 0 through N−1). Each symbol isassociated with respective symbol data (e.g., respective four-bit datavalues, such as 0000, 0001, 0010, etc.). As shown in FIG. 3B, eachsymbol is associated with a nominal center frequency in a frequency bandthat is 62.5 kHz wide. It is noted that the frequency band for symbol 2and the frequency band for symbol 3 are not contiguous. That is, thenominal center frequency of the frequency band immediately adjacent toand above the frequency band for symbol 2 is 10.419 kHz, but thisfrequency is not assigned to any of the N symbols. Accordingly, theassigned frequency bands, in aggregate, axe not contiguous. In someembodiments, lookup table 124 is used by a receiving system to identifysymbols from determined frequencies of received signal pulses, and inturn, units of data corresponding to the identified symbols (e.g., thefour-bit data values 0000, 0001, etc.).

In some embodiments, symbols in the predefined set of N symbols need notbe assigned to frequency bands in order. For example, although FIG. 3Cshows symbol S₀ assigned to a lower frequency hand than the frequencyband to which S_(i) is assigned, and S_(N) assigned to the highestfrequency band, in some cases a respective symbol S_(i) may be assignedto a higher frequency band than the frequency band to which the nextsymbol S_(i+1) is assigned. Table 1 provides an illustrative example ofsymbols in a predefined set of 8 symbols being assigned to frequencybands without regard to any particular ordering of the symbols.

TABLE 1 Frequency Band (MHz) Nominal Frequency (MHz) Symbol 4.7-4.9 4.8S₂ 9.1-9.3 9.2 S₃ 10.6-10.8 10.7 S₇ 11.4-11.6 11.5 S₀ 11.7-11.9 11.8 S₅14.7-14.9 14.8 S₁ 18.5-18.7 18.6 S₄ 20.0-20.2 20.1 S₆

In some embodiments, instead of assigning frequencies or frequency bandsto symbols, lookup tables 104 and 124 assign frequency differences(sometimes called frequency shifts) to symbols. In some embodiments, thedifference in frequency between a respective signal pulse and amost-recent prior signal pulse (e.g., with no intervening signal pulses)is used to represent a symbol. In some embodiments, a transmittingsystem prepares to transmit a first symbol by determining, using alookup table, a first frequency difference associated with the firstsymbol. In some embodiments, the transmitting system then transmits thefirst signal by transmitting a first signal pulse at a first frequency,and a second signal pulse at a second frequency, where the differencebetween the second frequency and the first frequency (or the absolutevalue of the difference) is the first frequency difference. In someembodiments, a receiving system receives a first signal pulse anddetermines a first frequency of the first signal pulse, and thenreceives a second signal pulse and determines a second frequency of thesecond signal pulse, where the difference between the second frequencyand the first frequency (or the absolute value of the difference) is arespective frequency difference. In some embodiment, the receivingsystem determines, using a lookup table, the symbol corresponding to thedetermined frequency difference. It is noted that where frequencydifferences are used to represent symbols instead of frequencies, thefrequency bands used to transmit signal pulses may or may not becontiguous, and may be widely separated rather than confined to a narrowfrequency range.

FIG. 3C is a conceptual diagram showing example allocations of afrequency spectrum 300, in accordance with some embodiments. Frequencyspectrum 300 includes a set of frequency bands associated with apredefined set of N symbols S₀ through S_(N−1). Each respective symbolin the predefined set is associated with a distinct frequency band inthe set of frequency bands in frequency spectrum 300. For example, asshown in FIG. 3C, frequency spectrum 300 includes non-contiguousfrequency bands 302, 304, 306, 308, 310, and 312. Frequency band 302 isassociated with (e.g., represents) symbol S₀; frequency band 304 isassociated with symbol S₁ frequency band 306 is associated with symbolS₂; frequency band 308 is associated with symbol S₃; frequency band 310is associated with symbol S₄; and frequency band 312 is associated withsymbol S_(N−1). The set of frequency bands (which includes frequencybands 302, 304, 306, 308, 310, and 312) associated with the predefinedset of N symbols, in aggregate, are not contiguous.

FIG. 3D illustrates an example sequence 320 of discrete-frequencysignals, in accordance with some embodiments in some embodiments,sequence 320 is transmitted by a transmitting system (e.g., transmittingsystem 120, FIG. 1, or transmitting system 200, FIG. 2A) or a componentof a transmitting system (e.g., transmitter 114, FIG. 1). In someembodiments, sequence 320 is received by a receiving system (e.g.,receiving system 140, FIG. 1, or receiving system 220, FIG. 2B) or acomponent of a receiving system (e.g., receiver 118, FIG. 1). Bachsignal pulse in the sequence represents a respective symbol of thepredefined set of N symbols based on the frequency of the signal pulse.For example, sequence 320 includes a first signal pulse 322 at a firstfrequency that represents symbol S₂, followed by a second signal pulse324 at a second frequency that represents symbol S₄, followed by a thirdsignal pulse 326 at a third frequency that represents symbol S₀,followed by a fourth signal pulse 328 at a fourth frequency thatrepresents symbol S₃. Sequence 320 optionally includes one or moreadditional signal pulses at respective frequencies representingrespective symbols in the predefined set of symbols.

FIG. 3E illustrates example variations in signal duration forrepresenting multiple symbols using a given frequency. In someembodiments, a first number of bits of information is represented by theparticular frequency of a given signal pulse. In some embodiments, asecond number of bits of information is represented by the length of asignal pulse at the particular frequency. For example, FIG. 3Eillustrates four signal pulses 330, 332, 334, and 336. Signal pulse 330has a frequency that represents a symbol S_(i). In addition, in theexample shown in FIG. 3E, the length of signal pulse 330 is one of fourpossible signal lengths and corresponds to data value “00.” As such,signal pulse 330 represents the information of symbol S in combinationwith two additional bits of information, “00.”

Signal pulse 332 in FIG. 3E has the same frequency as signal pulse 332and thus is also associated with the symbol S_(i). In addition, thelength of signal pulse 332 corresponds to data value “01.” As such,signal pulse 332 represents the information of symbol S_(i) incombination with two additional bits of information, “01.”

Likewise, signal pulse 334 has the same frequency as signal pulses 330and 332 and thus is also associated with the symbol S_(i). In addition,the length of signal pulse 334 corresponds to data value “10.” As such,signal pulse 334 represents the information of symbol S_(i) incombination with two additional bits of information, “10.”

Finally, signal pulse 336 has the same frequency as signal pulses 330,332, and 334, and thus is also associated with the symbol. In addition,the length of signal pulse 336 corresponds to data value “11.” As such,signal pulse 336 represents the information of symbol S_(i) incombination with two additional bits of information, “11.”

One of ordinary skill in the art will readily appreciate that any numberof different signal pulse lengths can be used to represent additionalinformation beyond the symbol represented by the signal frequency.

FIG. 4 is a block diagram illustrating an example implementation offrequency detection circuitry 400, in accordance with some embodiments.In some embodiments, frequency detection circuitry 400 corresponds to,or is part of, frequency determination circuitry 120 (FIG. 1), orfrequency detector 128 (FIG. 1). In some embodiments, frequencydetection circuitry 400 is used to detect the frequency of an inputsignal 401. In some embodiments, frequency detection circuitry includesone or more frequency detection stages 402.

Input signal 401 is received at a first frequency detection stage 402-1.In some embodiments, no delay (e.g., a delay of zero) is applied toinput signal 401 upon being received at frequency detection stage 402-1.In some embodiments, demodulator 404-1 in first frequency detectionstage 4024 compares received input signal 401 to respective frequenciesin a plurality of candidate frequency bands (or frequency ranges).Demodulator 4044 determines a particular first frequency band of thecandidate frequency bands that has the greatest degree of correlationwith input signal 401. The determined frequency first hand isinterpreted to be the frequency band in which the frequency of thereceived input signal 401 must exist. In some embodiments, the resultsof frequency detection stage 402-1 (e.g., the outputs of demodulator404-1) are provided to a signal processing block 408.

In some embodiments, input signal 401 is provided to second frequencydetection stage 404-2, which delays input signal 401 (e.g., with a firstamount of delay). The delayed input signal is provided to seconddemodulator 404-2. In some embodiments, the determined first frequencyband from demodulator 404-1 is subdivided into a second plurality of(narrower) candidate frequency bands. In some embodiments, signalprocessing block 408 receives the identification of the first frequencyband from frequency detection stage 4024, determines the subdivisions,and configures frequency detection stage 402-2 (or a component offrequency detection stage 402-2, such as demodulator 404-2) using thesecond plurality of candidate frequency bands. In some embodiments,second demodulator 404-2 compares the delayed input signal to respectivefrequencies in the second plurality of candidate frequency bands (e.g.,the subdivisions of the determined first frequency band from frequencydetection stage 4024). Second demodulator 404-2 determines a particularsecond frequency band (narrower than the first frequency band) of thesecond plurality of candidate frequency bands that has the greatestdegree of correlation with the delayed input signal. The determinedsecond frequency band is interpreted to be the frequency band in whichthe frequency of the received input signal 401 must exist.

One of ordinary skill will readily appreciate that any number M offrequency detection stages (e.g., up to and including frequencydetection stage 402-M) are used to determine the frequency of inputsignal 401 with increasingly greater accuracy, through successive delaysof input signal 401 and successive subdivision of frequency bandsdetermined by preceding stages into narrower candidate frequency bands,and comparison of the delayed input signals to the increasingly narrowercandidate frequency bands (e.g., by demodulators up to and includingdemodulator 404-M). In some embodiments, signal processing block 408obtains the identified frequency band of each preceding stage and usesthe identified frequency band to configure each successive frequencydetection stage with the narrowed set of candidate frequency bands basedon the identified frequency band.

In some embodiments, delays for successive frequency detection stagesincreases linearly. In some embodiment, delays for successive frequencydetection stages increase exponentially by a predefined multiple. Forexample, a first stage applies zero delay; a second stage applies afirst amount of delay; a third stage applies a second amount of delaythat is a predefined multiple M of the first amount of delay; a fourthstage applies a third amount of delay that is M² times the first amountof delay, etc.

FIGS. 5A-5C are flow diagrams illustrating an example method 500 ofreceiving information, in accordance with some embodiments. In someembodiments, and as described herein, method 500 is performed at asystem for information transfer (e.g., receiving system 140, FIG. 1, orreceiving system 220, FIG. 2B). In some embodiments, the system includesa receiver (e.g., receiver 118, FIG. 1), frequency discriminationcircuitry (e.g., frequency determination circuitry 116, FIG. 1), andprocessing circuitry (e.g., processing circuitry 122, FIG. 1). In someembodiments, the processing circuitry is implemented using one or moreprocessors (e.g., CPU(s) 222, FIG. 2B), and memory (e.g., memory 226,FIG. 2B) storing one or more programs for execution by the one or moreprocessors, the one or more programs including instructions forperforming operations described herein. In some embodiments, theprocessing circuitry is implemented using hardware circuitry such as oneor more field-programmable gate arrays (FPGAs) or application-specificintegrated circuits (ASICs) configured to perform the operationsdescribed herein. In some embodiments, the system includes or iselectrically coupled with a lookup table (e.g., lookup table 124, FIG.3B) storing a (first) predefined set of frequencies and/or frequencybands and a predefined set of symbols (e.g., bit patterns representingdata), where each frequency is associated with a respective symbol.

In some embodiments, at the system for information transfer (502),before receiving a first signal pulse, the system obtains (504) a thirdsignal pulse (e.g., for calibration). In some embodiments, the systemdetermines a third frequency of the third signal pulse and compares thethird frequency to a predefined calibration frequency to determine adifference between the third frequency and the predefined calibrationfrequency. In some embodiments, frequency detection circuitry of, orelectrically coupled with, the receiver is susceptible to measurementerrors, such as errors resulting from propagation delays or internalbiases within the frequency detection circuitry that may vary withenvironmental factors (e.g., ambient temperature changes, or temperaturechanges in one or more components in the frequency detection circuitry).In some embodiments, a calibration pulse at a predefined calibrationfrequency (e.g., the third signal pulse) is used to calibrate thefrequency detection circuitry to correct for such errors. Accordingly,in some embodiments, obtaining the third signal pulse includesgenerating the third signal pulse at the known predefined calibrationfrequency by the receiver, or by receiver-side signal generationcircuitry electrically coupled to the frequency detection circuitry. Insome such embodiments, the third signal pulse is not provided by thetransmitter.

In some embodiments, one or more additional pulses similar to the thirdsignal pulse can be generated (at the receiver side) and provided as aninput to the frequency detection circuitry. In some embodiments, thethird pulse and any additional pulses are generated during anticipatedgaps in received transmissions (e.g., times during which transmissionsare not expected to be received). In some embodiments, the third pulseand any additional pulses are generated periodically. In someembodiments, the third pulse and any additional pulses are generatedbased on a detected rate of change of temperature of the frequencydetection circuitry, or of the receiving system. In some embodiments,the third pulse and any additional pulses are generated based on adetected amount of time that the frequency detection circuitry, or thereceiving system, has been in operation (e.g., since being powered on).

In some embodiments, the system (e.g., the receiver, or frequencymeasurement circuitry) determines the frequency of the third signalpulse and compares it to the known and expected predefined calibrationfrequency, to determine an offset (e.g., positive or negative value)between the measured frequency and the expected frequency. In someembodiments, the offset represents the effect of the errors local to thereceiving system as described above. In some embodiments, the offset isapplied to adjust measured frequencies of subsequently received pulses(e.g., step 518), and frequency bands associated with the subsequentlyreceived pulses are determined from the offset-adjusted frequencies.

In some embodiments, a calibration pulse at a predefined calibrationfrequency is transmitted from a transmitter prior to transmitting one ormore signal pulses representing respective symbols. In some embodiments,the receiver treats an initial pulse in a series of pulses (e.g., apulse received after a predetermined timeout period since amost-recently-received signal pulse) as a calibration pulse, determinesthe frequency of the initial pulse, and compares the frequency of theinitial pulse to the predefined calibration frequency to determine anoffset (e.g., positive or negative value). In some embodiments, theoffset represents the effect of Doppler shift on the received pulse. Insome embodiments, the offset is applied to adjust measured frequenciesof subsequently received pulses, and frequency bands associated with thesubsequently received pulses are determined from the offset-adjustedfrequencies. In some embodiments, a series of calibration pulses atdifferent calibration frequencies are transmitted (e.g., prior totransmitting the one or more signal pulses), and the receiver compareseach received calibration pulse to a set of predefined calibrationfrequencies to determine respective offsets at each of the predefinedcalibration frequencies. In some embodiments, the series of calibrationpulses are transmitted uninterrupted by transmission of signal pulsesrepresenting respective symbols. In some embodiments, one or morecalibration pulses are transmitted in between transmission of signalpulses representing respective symbols (e.g., calibration pulses arealternated, or otherwise interleaved, with signal pulses representingsymbols).

The system receives (506) a first signal pulse (e.g., a respectivesignal pulse as shown in and described herein with reference to FIG.3D). In some embodiments, a duration of the first signal pulse is lessthan a predetermined duration (508). For example, the duration of thefirst signal pulse is less than 1 μs. In some embodiments, a duration ofthe first signal pulse includes at least one full period (of a wave) atthe first frequency. In some embodiments, a duration of the first signalpulse is less than one full period at the first frequency.

In some embodiments, the first signal pulse is received (510) at aplurality of input channels of a receiver, each input channel associatedwith a respective frequency band in a first predefined set of frequencybands.

The system determines (512) a first frequency band associated with thefirst signal pulse. In some embodiments, a length of the first signalpulse is less (514) than one full wavelength. In some embodiments, thesystem determines a phase of the first signal pulse at a respectivetime. In some embodiments, the determined phase corresponds to azero-crossing of the first signal pulse. In some embodiments, the systemdetermines a first frequency of the first signal pulse based on thedetermined phase of the first signal pulse at the respective time and ona rate of change with respect to time (e.g., slope) of the first signalpulse at the respective time. In some embodiments where the determinedphase corresponds to a zero-crossing of the first signal pulse, thefirst frequency of the first signal pulse is determined based on theslope (which can be either positive or negative) of the first signalpulse at the zero-crossing. In some embodiments, the system determinesthat the first frequency of the first signal pulse is in the firstfrequency band.

In some embodiments, determining the first frequency band associatedwith the first signal pulse includes measuring (516) channel power ofeach respective input channel and identifying a respective input channelhaving a highest measured channel power. In some embodiments, the firstfrequency band is the respective frequency band associated with theidentified input channel.

In some embodiments, determining the first frequency band of the firstsignal pulse includes (518) determining an initial frequency of thefirst signal pulse, determining an adjusted frequency of the firstsignal pulse based on applying the determined difference (e.g.,determined in step 504) to the initial frequency, and determining thefirst frequency band based on the adjusted frequency.

In some embodiments, determining the first frequency band associatedwith the first signal pulse comprises using cascaded instantaneousfrequency measurement (IFM) (e.g., as described herein with reference toFIG. 4). In some embodiments, the system receives (520) the first signalpulse (e.g., input signal 401, FIG. 4) at a first frequency detectionstage (e.g., first frequency detection stage 402-1, FIG. 4). In someembodiments, the system determines, using the first frequency detectionstage, a first frequency range that includes the first frequency of thefirst signal pulse (e.g., a first range of possible frequencies of thefirst signal pulse). In some embodiments, after determining the firstfrequency range, the system receives the first signal pulse at a secondfrequency detection stage (e.g., second frequency detection stage 402-2,FIG. 4) (e.g., by delaying the first signal pulse, and receiving thedelayed first signal pulse at the second frequency detection stage). Insome embodiments, the system determines, within the first frequencyrange, using the second frequency detection stage, a second frequencyrange that includes the first frequency of the first signal pulse. Insome embodiments, the second frequency range is smaller than the firstfrequency range. In some embodiments, the first frequency bandcorresponds to the second frequency range.

In some embodiments, any number of additional frequency detection stages(e.g., through frequency detection stage 402-M, FIG. 4) are used, whereeach subsequent frequency detection stage is used to farther narrow thepossible range of the frequencies of the first signal pulse, todetermine a sufficiently narrow frequency band that necessarily includesthe frequency of the received signal. In some embodiments, a frequencyband determined by a respective frequency detection stage issufficiently narrow when it corresponds to only one frequency band inthe first predefined set of frequency bands, such that a representedsymbol can be determined. For example, a subsequent (e.g., third,fourth, fifth, etc.) frequency detection stage narrows the secondfrequency range to a frequency range that includes substantially thesame frequencies as (e.g., at least 90%, 95%, or 98% overlap, etc.), oris smaller than, a respective frequency band in the first predefined setof frequency bands. In this example, the first frequency band isdetermined to be the respective frequency band. In some embodiments, thefrequencies, or frequency bands, of calibration signal pulses and/orsignal pulses representing symbols are determined using this approach.In some embodiments, the first, second, and any other frequencydetection stages together form at least a portion of frequency detectioncircuitry that is part of, or in some embodiments electrically coupledwith, a receiver. In some embodiments, a processing module or processingcircuitry (e.g., signal processing block 408, FIG. 4) is used toconfigure the candidate frequencies considered by a respectivesubsequent frequency stage based on results determined (e.g., afrequency band identified) at a respective preceding frequency stage.

In accordance with a determination that the first frequency band is arespective frequency band in the first predefined set of frequency bands(522), the system determines (524), from a predefined set of symbols, afirst symbol associated with the first frequency band and represented bythe first signal pulse.

In some embodiments, the first predefined set of frequency bandsincludes a plurality of frequency bands. In some embodiments, the firstfrequency is determined to be a nominal (e.g., center) frequency in thefirst frequency band, or within a predefined threshold (e.g., within 1%,5%, 7% or 10%) of the nominal frequency in the first frequency band. Forexample, as described with reference to FIGS. 3A-3B the frequenciesassociated with symbols are center frequencies in their respective 62.5kHz frequency bands.

In some embodiments, the first predefined set of frequency bands isassociated (526) with the predefined set of symbols using a lookup table(e.g., lookup table 124, FIG. 3B). For example, the lookup table mapseach frequency band in the first predefined set of frequency bands to adistinct respective symbol in the predefined set of symbols. In someembodiments, determining the first symbol associated with the firstfrequency band includes selecting the respective symbol associated withthe first frequency band in the lookup table.

In some embodiments, the predefined set of symbols includes (528) two ormore symbols associated with the first frequency band, each symbol ofthe two or more symbols associated with a respective pulse duration. Insome embodiments, the system determines a first pulse duration of thefirst signal pulse. In some embodiments, determining the first symbolincludes selecting the first symbol from the two or more symbolsassociated with the first frequency band based on the first pulseduration. For example, the system selects the symbol in the two or moresymbols whose associated pulse duration (sometimes called pulse width)corresponds to the first pulse duration of the first signal pulse. Forexample, as described herein with reference to FIG. 3E, a respectivefrequency, or frequency hand, is associated with four symbols (e.g.,distinguished by the additional information 00, 01, 10, and 11), and therespective frequency is associated with a nominal pulse duration (e.g.,900 μs). In this example, a signal at the respective frequency can betransmitted using a pulse duration of 800 ns, 850 ns, 900 ns, or 950 ns.At the respective frequency, these pulse durations represent the symbols00, 01, 10, and 11, respectively. Thus, for example, a received signalat the respective frequency having a pulse duration of 950 ns isinterpreted as the symbol 11. Altering the pulse duration of thetransmitted pulse enables a given frequency to represent additional bitsof information.

In some embodiments, the predefined set of symbols includes a pluralityof symbols. In some embodiments, both the frequency and the representedsymbol are determined from the same first signal pulse (e.g., the same(entire) portion of the signal), in contrast to implementations wherefrequency of a carrier signal must first be determined from a firstportion of the carrier signal prior to, god separately from, determiningone or more symbols from a second, subsequent, portion of the carriersignal.

In some embodiments, the first predefined set of frequency bandsincludes (530) a first respective frequency band and a second respectivefrequency band that is a nearest frequency band in the first predefinedset of frequency bands to the first respective frequency band. In someembodiments, the first respective frequency band has a first centerfrequency. In some embodiments, the second respective frequency band hasa second center frequency. In some embodiments, a difference between thefirst center frequency and the second center frequency exceeds apredefined frequency difference threshold. In some embodiments, theseparation of a respective frequency band from its nearest frequencyband in a predefined set of frequency bands, such as the firstpredefined set of frequency bands, accounts for potential Doppler shiftof a signal transmitted at the center frequency of the respectivefrequency band, as a result of a non-zero relative velocity between thereceiver and a transmitter transmitting the signal.

In some embodiments, a maximum Doppler shift is estimated based on arespective (center) frequency, a maximum estimated velocity of thereceiver, and a maximum estimated velocity of the transmitter (e.g., thenegative of the maximum velocity of the receiver, due to the transmittermoving in the opposite direction from the receiver). In other words, themaximum. Doppler shift can be estimated based on the respective (center)frequency and two times a maximum possible speed of a transmitter orreceiver (or of a vehicle or craft carrying the transmitter orreceiver). In some embodiment, the predefined frequency differencethreshold is large enough such that when a signal at a center frequencyof a respective frequency band is transmitted, even with the maximumDoppler shift, the receiver can determine the signal's intendedfrequency band. In some cases, the frequency of the received signal,even with the maximum Doppler shift, is still within the intendedfrequency band. In some cases, the frequency of the received signal,even with the maximum Doppler shift, falls closer to the intendedfrequency band than to any other frequency band in the predefined set offrequency bands. In some embodiments, nearest frequency bands in thepredefined set of frequency bands are sufficiently separated (e.g., byat least the predefined frequency difference threshold) such that anestimated maximum Doppler shift would not result in one symbol beingmistaken for another. In some embodiments, the receiver need not accountfor (or attempt to account for) Doppler shift in received signals. Insome embodiments, the predefined set of frequency bands are selected soas to obtain this benefit.

Furthermore, as one of ordinary skill in the art will appreciate,implementations where the predefined set of frequency bands are notcontiguous enable separation of even relatively narrow frequency bands,in which case spectral efficiency can remain high while transmissionerrors due to Doppler shift are reduced or even eliminated. By contrast,in implementations requiring continuous spectrum, frequency bands wouldneed to be widened in order to enable a receiver to forgo accounting forDoppler shift; which would reduce spectral efficiency.

The system provides (532) the first symbol. In some embodiments, thefirst symbol is used by one or more processors or processing modules forinterpreting data represented by the first symbol. In some embodiments,the first symbol is, or represents, a first unit of information, such asa first bit pattern (e.g., a pattern of one or more bits), and the oneor more processors interpret the information (e.g., bit pattern) of thefirst symbol, optionally in conjunction with one or more other units ofinformation (e.g., bit patterns) of one or more other symbols, tointerpret the data received.

In some embodiments, each frequency band in the first predefined set offrequency bands is associated (534) with a distinct respective symbol inthe predefined set of symbols. In some embodiments, each respectivesymbol in the predefined set of symbols represents a distinct respectiveunit of information (e.g., a distinct bit pattern). In some embodiments,frequency bands in the first predefined set of frequency bands, inaggregate, are (536) not contiguous (e.g., as described herein withreference to FIGS. 3A-3C). In some embodiments, each frequency band isrepresented by a nominal frequency within the respective frequency band(e.g., the center frequency within the respective frequency band). Insome embodiments, the first predefined set of frequency bands span atleast two distinct ranges of frequencies separated by at least one rangeof frequencies (e.g., one frequency band) that is not part of the set ofpredefined frequency bands (e.g., as described herein with reference toFIGS. 3A-3B).

In some embodiments, after at least a predefined amount of time sincereceiving the first signal pulse, the system receives (538) a secondsignal pulse. In some embodiments, the predefined amount of time ismeasured from the time that (receipt of) the first signal pulse ends. Insome embodiments, the predefined amount of time is measured from thetime that the first signal pulse was initially received, and thepredefined amount of time is longer than the duration of the firstsignal pulse, such that the second signal pulse is initially receivedafter an amount of time after receipt of the first signal pulse ends. Insome embodiments, the system determines (540) a second frequency handassociated with the second signal pulse. In accordance with adetermination that the second frequency band is a respective frequencyband in the first predefined set of frequency bands (542), the systemdetermines, from the predefined set of symbols, a second symbolassociated with the second frequency band and represented by the secondsignal pulse, and provides the second symbol. In some embodiments, thesecond symbol is provided to one or more processors or processingmodules for interpreting data represented by the second symbol. In someembodiments, the second symbol represents a bit pattern (e.g., a patternof one or more bits), and the one or more processors interpret the bitpattern represented by the second symbol, optionally in conjunction withone or more other bit patterns represented by one or more other symbols(e.g., the first symbol), to interpret the data received.

In some embodiments, after receiving the first signal pulse, the systemreceives (544) a control signal (e.g., via a control channel, using apredefined control frequency band (known also to a transmitter))associating a second predefined set of frequency bands with thepredefined set of symbols. In some embodiments, the second predefinedset of frequency bands is distinct from the first predefined set offrequency bands. In some embodiments, each frequency band in the secondpredefined set of frequency bands is associated with a distinctrespective symbol in the predefined set of symbols. In some embodiments,at least one symbol in the predefined set of symbols is assigned to afrequency band in the second predefined set of frequency bands that isdifferent from the frequency band in the first predefined set offrequency bands to which the symbol was assigned. In some embodiments,frequency bands in the second predefined set of frequency bands, inaggregate, are not contiguous.

In some embodiments, after receiving the control signal, the systemreceives (546) a fourth signal pulse. In some embodiment, the systemdetermines a third frequency band associated with the fourth signalpulse. In some embodiments, in accordance with a determination that thethird frequency band is a respective frequency band in the secondpredefined set of frequency bands, the system determines, from thepredefined set of symbols, a third symbol associated with the thirdfrequency band and represented by the fourth signal pulse, and providesthe third symbol.

It should be understood that the particular order in which theoperations in method 500 have been described is merely an example and isnot intended to indicate that the described order is the only order inwhich the operations could be performed. One of ordinary skill in theart would recognize various ways to re-order the operations describedherein. Additionally, it should be noted that details of other processesdescribed herein with respect to other methods described herein (e.g.,method 600) are also applicable in an analogous manner to method 500described above with respect to FIGS. 5A-5C. For example, the signalpulses, symbols, unit of data, frequencies, and frequency bandsdescribed above with reference to method 500 optionally have one or moreof the characteristics of the signal pulses, symbols, units of data,frequencies, and frequency bands described herein with reference toother methods described herein (e.g., method 600). For brevity, thesedetails are not repeated here.

FIGS. 6A-6B are flow diagrams illustrating an example method 600 oftransmitting information, in accordance with some embodiments. In someembodiments, and as described herein, method 600 is performed at asystem for information transfer (e.g., transmitting system 120, FIG. 1,or transmitting system 200, FIG. 2A). In some embodiments, the systemincludes a transmitter (e.g., transmitter receiver 114, FIG. 1),frequency generation circuitry (e.g., frequency generation circuitry106, FIG. 1), and processing circuitry (e.g., processing circuitry 102,FIG. 1). In some embodiments, the processing circuitry is implementedusing one or more processors (e.g., CPU(s) 202, FIG. 2A), and memory(e.g., memory 206, FIG. 2A) storing one or more programs for executionby the one or more processors, the one or more programs includinginstructions for performing operations described herein. In someembodiments, the processing circuitry is implemented using hardwarecircuitry such as one or more field-programmable gate arrays (FPGAs) orapplication-specific integrated circuits (ASICs) configured to performthe operations described herein. In some embodiments, the systemincludes or is electrically coupled with a lookup table (e.g., lookuptable 104, FIG. 3A) storing a predefined set of symbols (e.g., bitpatterns representing data) and a (first) predefined set of frequenciesand/or frequency bands, where each symbol is associated with arespective frequency.

At the system for information transfer (602), the system transmits (604)a plurality of successive pulses having one or more calibrationfrequencies. For example, a first pulse of the plurality of successivepulses corresponds to the third signal pulse, as described in step 504of method 500.

The system obtains (606) a first symbol, in a predefined set of symbols,for transmission (e.g., a respective symbol in the predefined set of Nsymbols S₀ through S_(N−1), as described herein with reference to FIGS.3A-3D). In some embodiments, the first symbol represents a first unit ofinformation. In some embodiments, the predefined set of symbols includes(608) two or more symbols associated with the first frequency band, eachsymbol of the two or more symbols associated with a respective pulseduration (e.g., as described herein with reference to FIG. 3E).

The system determines (610) a first frequency band, in a firstpredefined set of frequency bands, associated with the first symbol.

In some embodiments, each frequency band in the first predefined set offrequency bands is associated (612) with a distinct respective symbol inthe predefined set of symbols. In some embodiments, each respectivesymbol in the predefined set of symbols represents a distinct respectiveunit of information (e.g., a distinct bit pattern). In some embodiments,frequency bands in the first predefined set of frequency bands, inaggregate, are (614) not contiguous (e.g., as described herein withreference to FIGS. 3A-3C). In some embodiments, the transmitter receivesinformation for transmission, and identifies for transmission one ormore symbols representing the information (e.g., each symbolrepresenting a respective unit of the information).

In some embodiments, the first predefined set of frequency bands isassociated (616) with the predefined set of symbols using a lookup table(e.g., lookup table 104, FIG. 3A) (e.g., the lookup table maps eachfrequency band in the first predefined set of frequency bands to adistinct respective symbol in the predefined set of symbols). In someembodiments, determining the first frequency band associated with thefirst symbol includes selecting the respective frequency band associatedwith the first symbol in the lookup table.

The system transmits (618) a first signal pulse having a first frequencyin the first frequency band (e.g., a nominal frequency, such as a centerfrequency, in the first frequency band). In some embodiments, arespective transmitted signal pulse, such as the first signal pulse, istransmitted using a predefined maximum transmission power level (e.g.,associated with a predefined maximum signal amplitude). In someembodiments, a respective transmitted signal pulse is transmitted usinga transmission power level that is at least a predefined threshold powerlevel with respect to a predefined maximum transmission power level(e.g., of a transmitter). For example, a respective transmitted signalpulse is transmitted using a transmission power level that is at least80%, 90%, or 95%, etc. of the predefined maximum transmission powerlevel of a transmitter. In some embodiments, any respective transmittedsignal pulse representing any respective symbol in the first predefinedset of frequency bands can be transmitted using the predefined maximumtransmission power level, or using a transmission power level that is atleast the predefined threshold power level with respect to thepredefined maximum transmission power level, thereby improving thesignal-to-noise ratio of transmitted signals.

In some embodiments, the system determines (620) a first pulse durationbased on the first symbol of the two or more symbols (e.g., describedwith respect to step 604). In some embodiments, a pulse duration of thefirst signal pulse corresponds to the first pulse duration.

In some embodiments, the system obtains (624) a second symbol, in thepredefined set of symbols, for transmission. In some embodiments, thesystem determines a second frequency band, in the first predefined setof frequency bands, associated with the second symbol. In someembodiments, after at least a predefined amount of time sincetransmitting the first signal pulse, the system transmits a secondsignal pulse having a second frequency in the second frequency band(e.g., a nominal frequency, such as a center frequency, in the secondfrequency band). In some embodiments, the predefined amount of time ismeasured from the time that (transmission of) the first signal pulseends. In some embodiments, the predefined amount of time is measuredfrom the time that transmission of the first signal pulse was initiated,and the predefined amount of time is longer than the duration of thefirst signal pulse, such that transmission of the second signal pulsebegins after an amount of time after transmission of the first signalpulse ends.

In some embodiments, after transmitting the first signal pulse, thesystem transmits (626) (e.g., via a control channel, using a predefinedcontrol frequency band (known also to a receiver)) a control signalassociating a second predefined set of frequency bands with thepredefined set of symbols. In some embodiments, the second predefinedset of frequency bands is distinct from the first predefined set offrequency bands. In some embodiments, each frequency band in the secondpredefined set of frequency bands is associated with a distinctrespective symbol in the predefined set of symbols. In some embodiments,at least one symbol in the predefined set of symbols is assigned to afrequency band in the second predefined set of frequency bands that isdifferent from the frequency band in the first predefined set offrequency bands to which the symbol was assigned. In some embodiments,frequency bands in the second predefined set of frequency bands, inaggregate, are not contiguous.

In some embodiments, after transmitting the control signal, the systemobtains (628) a third symbol, in the predefined set of symbols, fortransmission. In some embodiments, the system determines a thirdfrequency band, in the second predefined set of frequency bands,associated with the third symbol. In some embodiments, the systemtransmits a third signal pulse having a third frequency in the thirdfrequency band.

In some embodiments, prior to transmitting the control signalassociating the second predefined set of frequency bands with thepredefined set of symbols, the system determines (630) that a spectraldensity (e.g., a power spectral density) of a respective frequency bandin the first predefined set of frequency bands satisfies (e.g., meets orexceeds) a predefined threshold value. In some embodiments, the systemidentifies, from the predefined set of symbols, a respective symbol thatis associated with the respective frequency band (whose spectral densitysatisfies the predefined threshold value) in the first predefined set offrequency bands. In some embodiments, the system determines that aspectral density of a fourth frequency band, outside of the firstpredefined set of frequency bands, is below the predefined thresholdvalue (e.g., a different frequency band that is not currently one of thepredefined set of frequency bands, and thus not already being used for arespective symbol). In some embodiments, the second predefined set offrequency bands includes the fourth frequency band, and the respectivesymbol in the predefined set of symbols (that was associated with therespective frequency band in the first predefined set of frequency bandswhose spectral density satisfies the predefined threshold value) isassociated with the fourth frequency band in the second predefined setof frequency bands. Stated another way, in some embodiments, aparticular band in the first predefined set of frequency bands may bedetermined to have a spectral density that is too high. In someembodiments, spectral density above a predefined threshold valueindicates that the particular frequency band is “noisy” and/or that toomany other signals are being transmitted using the associated frequencyband. Accordingly, in some embodiments, a new frequency band withsufficiently low spectral density (e.g., a “quieter” frequency band) isidentified as a potential replacement for the noisy frequency band. Insome embodiments, the symbol-to-frequency assignments are modified sothat the symbol represented by the noisy frequency band is insteadrepresented by the new quieter frequency band. In some embodiments, atransmitting system communicates the modified assignments (e.g., usingthe second predefined set of frequency bands) to a receiving system andthen proceeds to transmit information using the modified assignments.

It should be understood that the particular order in which theoperations in method 600 have been described is merely an example and isnot intended to indicate that the described order is the only order inwhich the operations could be performed. One of ordinary skill in theart would recognize various ways to re-order the operations describedherein. Additionally, it should be noted that details of other processesdescribed herein with respect to other methods described herein (e.g.,method 500) are also applicable in an analogous manner to method 600described above with respect to FIGS. 6A-6B. For example, the signalpulses, symbols, units of data, frequencies, and frequency bandsdescribed above with reference to method 600 optionally have one or moreof the characteristics of the signal pulses, symbols, units of data,frequencies, and frequency bands described herein with reference toother methods described herein (e.g., method 500). For brevity, thesedetails are not repeated here.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are offered by way of example only, andare not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Many modifications and variations are possiblein view of the above teaching without departing from their spirit andscope, as will be apparent to those skilled in the art. The embodimentswere chosen and described in order to best explain the principles of theinvention and its practical applications, to thereby enable othersskilled in the art to best use the invention and various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A method of receiving information, comprising:receiving a first signal pulse; determining a first frequency bandassociated with the first signal pulse; and in accordance with adetermination that the first frequency band is a respective frequencyband in a first set of frequency bands: determining, from a predefinedset of symbols associated with the first set of frequency bands, a firstsymbol associated with the first frequency band and represented by thefirst signal pulse; wherein: the first set of frequency bands includes asecond frequency band that is a nearest frequency band in the first setof frequency bands to the first frequency band; the first frequency bandhas a first center frequency; the second frequency band has a secondcenter frequency; and a difference between the first center frequencyand the second center frequency exceeds a frequency differencethreshold.
 2. The method of claim 1, wherein the frequency differencethreshold is based on a Doppler shift determined using a thresholdvelocity of a transmitter transmitting the first signal pulse and athreshold velocity of a receiver receiving the first signal pulse. 3.The method of claim 1, wherein, for each respective frequency band inthe first set of frequency bands: the respective frequency band has afirst respective center frequency; a nearest frequency band in the firstset of frequency bands to the respective frequency band has a secondrespective center frequency; and a difference between the firstrespective center frequency of the respective frequency band and thesecond respective center frequency of the nearest frequency band exceedsa respective frequency difference threshold corresponding to therespective frequency band.
 4. The method of claim 1, wherein eachfrequency band in the first set of frequency bands is associated with adistinct respective symbol in the predefined set of symbols.
 5. Themethod of claim 1, wherein: the first set of frequency bands isassociated with the predefined set of symbols using a lookup table; anddetermining the first symbol associated with the first frequency bandincludes selecting the respective symbol associated with the firstfrequency band in the lookup table.
 6. The method of claim 1, including,before receiving the first signal pulse: receiving a second signalpulse; determining a second frequency of the second signal pulse;comparing the second frequency to a predefined calibration frequency todetermine a difference between the second frequency and the predefinedcalibration frequency; wherein determining the first frequency bandassociated with the first signal pulse includes: determining an initialfrequency of the first signal pulse; determining an adjusted frequencyof the first signal pulse based on applying the determined difference tothe initial frequency; and determining the first frequency baud based onthe adjusted frequency.
 7. The method of claim 1, including, afterreceiving the first signal pulse: receiving a control signal associatinga second set of frequency bands with the predefined set of symbols,wherein the second set of frequency bands is distinct from the first setof frequency bands; after receiving the control signal, receiving athird signal pulse; determining a third frequency band associated withthe third signal pulse; and in accordance with a determination that thethird frequency band is a respective frequency band in the second set offrequency bands: determining, from the predefined set of symbols, athird symbol associated with the third frequency band and represented bythe third signal pulse.
 8. The method of claim 7, wherein, for eachrespective frequency band in the second set of frequency bands: therespective frequency band has a first respective center frequency; anearest frequency band in the second set of frequency bands to therespective frequency band has a second respective center frequency; anda difference between the first respective center frequency of therespective frequency band and the second respective center frequency ofthe nearest frequency band exceeds a respective frequency differencethreshold corresponding to the respective frequency band.
 9. The methodof claim 1, wherein frequency bands in the first set of frequency bands,in aggregate, are not contiguous, and determining the first frequencyband associated with the first signal pulse includes: determining afirst frequency of the first signal pulse; and determining that thefirst frequency is closest to the first frequency band in the first setof frequency bands.
 10. The method of claim 1, wherein determining thefirst frequency band associated with the first signal pulse includesdetermining that a frequency of the first signal pulse is within thefirst frequency band.
 11. A system for information transfer, comprising:a receiver, configured to receive a first signal pulse; frequencydetermination circuitry, configured to determine a first frequency bandassociated with the first signal pulse; and processing circuitry,configured to: in accordance with a determination that the firstfrequency band is a respective frequency band in a first set offrequency bands: determine, from a predefined set of symbols associatedwith the first set of frequency bands, a first symbol associated withthe first frequency band and represented by the first signal pulse;wherein: the first set of frequency bands includes a second frequencyband that is a nearest frequency band in the first set of frequencybands to the first frequency band; the first frequency band has a firstcenter frequency; the second frequency band has a second centerfrequency; and a difference between the first center frequency and thesecond center frequency exceeds a frequency difference threshold.
 12. Amethod of transmitting information, comprising: obtaining a firstsymbol, in a predefined set of symbols, for transmission; determining afirst frequency band, in a first set of frequency bands associated withthe predefined set of symbols, that is associated with the first symbol;and transmitting a first signal pulse having a first frequency in thefirst frequency band; wherein: the first set of frequency bands includesa second frequency band that is a nearest frequency band in the firstset of frequency bands to the first frequency band; the first frequencyband has a first center frequency; the second frequency band has asecond center frequency; and a difference between the first centerfrequency and the second center frequency exceeds a frequency differencethreshold.
 13. The method of claim 12, wherein the frequency differencethreshold is based on a Doppler shift determined using a thresholdvelocity of a transmitter transmitting the first signal pulse and athreshold velocity of a receiver receiving the first signal pulse. 14.The method of claim 12, wherein, for each respective frequency band inthe first set of frequency bands: the respective frequency band has afirst respective center frequency; a nearest frequency band in the firstset of frequency bands to the respective frequency band has a secondrespective center frequency; and a difference between the firstrespective center frequency of the respective frequency band and thesecond respective center frequency of the nearest frequency band exceedsa respective frequency difference threshold corresponding to therespective frequency band.
 15. The method of claim 12, wherein eachfrequency band in the first set of frequency bands is associated with adistinct respective symbol in the predefined set of symbols.
 16. Themethod of claim 12, wherein: the first set of frequency bands isassociated with the predefined set of symbols using a lookup table; anddetermining the first frequency band associated with the first symbolincludes selecting the respective frequency band associated with thefirst symbol in the lookup table.
 17. The method of claim 12, including,after transmitting the first signal pulse: transmitting a control signalassociating a second set of frequency bands with the predefined set ofsymbols, wherein the second set of frequency bands is distinct from thefirst set of frequency bands; after transmitting the control signal,obtaining a second symbol, in the predefined set of symbols, fortransmission; determining a third frequency band, in the second set offrequency bands, associated with the second symbol; and transmitting asecond signal pulse having a frequency in the third frequency band. 18.The method of claim 17, wherein, for each respective frequency band inthe second set of frequency bands: the respective frequency band has afirst respective center frequency; a nearest frequency band in thesecond set of frequency bands to the respective frequency band has asecond respective center frequency; and a difference between the firstrespective center frequency of the respective frequency band and thesecond respective center frequency of the nearest frequency band exceedsa respective frequency difference threshold corresponding to therespective frequency band.
 19. A system for information transfer,comprising: processing circuitry, configured to: obtain a first symbol,in a predefined set of symbols, for transmission; determine a firstfrequency band, in a first set of frequency bands associated with thepredefined set of symbols, that is associated with the first symbol; anda transmitter, configured to transmit a first signal pulse having afirst frequency in the first frequency band; wherein: the first set offrequency bands includes a second frequency band that is a nearestfrequency band in the first set of frequency bands to the firstfrequency band; the first frequency band has a first center frequency;the second frequency band has a second center frequency; and adifference between the first center frequency and the second centerfrequency exceeds a frequency difference threshold.